runtime: avoid runtimeNano call on a common netpoll path
runtimeNano is slower than nanotime, so pass the duration
to runtime_pollSetDeadline as is. netpoll can add nanotime itself.
Arguably a bit simpler because, say, a negative duration
clearly represents already expired timer, no need to compare to
nanotime again.
This may also fix an obscure corner case when a deadline in past
which happens to be nanotime 0 is confused with no deadline at all,
which are radically different things.
Also don't compute any durations and times if Time is zero
(currently we first compute everything and then reset d back to 0,
which is wasteful).
name old time/op new time/op delta
TCP4OneShotTimeout-6 17.1µs ± 0% 17.0µs ± 0% ~ (p=0.421 n=5+5)
SetReadDeadline-6 230ns ± 0% 205ns ± 1% -10.63% (p=0.008 n=5+5)
Change-Id: I2aad699270289a5b9ead68f5e44ec4ec6d96baa0
Reviewed-on: https://go-review.googlesource.com/c/146344 Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Dmitry Vyukov <dvyukov@google.com>